Euphemism

Saying in a soft, indirect, or disguised way something harsh, ugly, or forbidden to name.

In Demons

After all, I cannot marry "other people's sins"!

What Stepan avoids saying, that the bride had something to do with Nikolai, he covers with "other people's sins." The quotation marks show that the expression is borrowed and that it serves to hold the subject without touching it.

Part One: Threads Come Together, Stepan Trofimovich

Nikolai Vsevolodovich, some captain or other [...] does not stop writing me indecent letters [...] If he really is your relative, forbid him to offend me and free me from these annoyances.

Part Two: The Town in Disorder, Lizaveta Nikolaevna